The paper titled “Improvement of landfill leachate biodegradability with ultrasonic process” has been retracted as it is essentially identical in title and technical content with a previously published paper “Mahvi AH, Roodbari AA, Nabizadeh Nodehi R, Nasseri S, and Dehghani MH et al. (2012), Improvement of landfill leachate biodegradability with ultrasonic process, PLoS ONE 7(7): e27571.doi: 10.1371/journal.pone.0027571,” [1] and it was found of significant similarity with the published article “A. Roodbari, R. Nabizadeh Nodehi, A. H. Mahvi, S. Nasseri, M. H. Dehghani, and M. Alimohammadi, Use of a sonocatalytic process to improve the biodegradability of landfill leachate,” Braz. J. Chem. Eng. vol. 29 no. 2 São Paulo Apr./June 2012, http://dx.doi.org/10.1590/S0104-66322012000200003.